1. Field of the Invention
The present invention relates to heat cooking apparatuses for example microwave oven, range oven and toaster oven, and more particularly, to a heat cooking apparatus which detects the smell emitted from food to determine the kind of food and the state of the cooked dish.
2. Description of the Background Art
In recent years, heat cooking apparatuses such as microwave oven have multiple functions including defrosting by microwave-heating, heat cooking, oven cooking and grill cooking by a heater etc. In addition, a users' need for simplifying household chores has created a big demand for automatic oven capable of cooking food conveniently, easily and quickly. Therefore, microwave ovens have been put to practical use in which heating time and adjustment of fire (microwave output or heat output) are automatically controlled by using a sensor for food of any kind and any quantity.
FIG. 5 is a sectional view showing a schematic structure of a conventional microwave oven.
With reference to FIG. 5, the microwave oven 60 includes a main body 1 of the cooking apparatus, the main body 1 having a heating chamber 2 provided therein for cooking food 13 by heating. Provided in the bottom portion of the heating chamber 2 is a turn table 3 on which the food 13 is put and which is rotated at the start of cooking of the oven 60, and provided in the upper portion of the heating chamber 2 is a magnetron 4 for supplying microwaves into the heating chamber 2. Provided at the rear portion of the heating chamber 2 are a heater 5 and a fan 6 for heating convection.
Further provided in the oven 60 is a sensor for use to control cooking of the food 13 as described as follows. That is, provided are a state of cooked food sensor 8 for sensing the state of cooked food 13, a weight sensor 9 provided in connection with the turn table 3 for sensing weight of the food 13 on the table 3, a temperature sensor 10 for sensing a temperature in the heating chamber 2 at the time of oven cooking or grill cooking, and a temperature sensor 11 for sensing the ambient temperature of the oven 60. The oven 60 is further provided with an air outlet 15 and a passage 16 for permitting atmospheric flow 14 evaporated from the food 13 in the heating chamber 2 to be discharged outside the chamber 2. The air outlet 15 is disposed in the rear portion of the main body 1, while the passage 16 is disposed to lead the atmospheric flow 14 in the chamber 2 to the air outlet 15.
The above-described sensor 8 is provided in the passage 16 to sense the atmospheric flow 14 passing through the passage 16, based on which sensing a state of the cooked food 13 is determined and based on which sensing output the degree of heating for cooking the food 13 is successively adjusted. Sensing methods of the sensor 8 include (1) a method of sensing, by using a thermistor, a rise of the atmospheric temperature caused by heating of food, (2) a method of sensing, by using a moisture sensor, a change in the amount of vapor generated by the heating of food and (3) a method of sensing, by using an infrared sensor, a change in the temperature of the food surface caused by the heating of the food.
Practically used as the weight sensor 9 include a sensor using a strain gauge and an electrostatic piezoelectric sensor.
Much importance is placed also on safety of heat cooking apparatuses. For example, when the food 13 is overheated to take fire (generation of smoke) due to defect of the microwave oven 60, heating portions such as the magnetron 4 and the heater 5 should be immediately stopped for safety. As a safety device in such a case, a thermofuse or the like is commonly used which cuts off power supply to the above-mentioned heating portions according to the output of the sensor 10 when the temperature in the heating chamber 2 exceeds a predetermined temperature.
When a user uses the above-described microwave oven 60 to cook food 13, first he distinguishes the kind of the food 13 and operates an external switch (not shown) provided on the front surface of the microwave oven 60 to designate the kind of food 13. Then, a microcomputer (not shown) contained in the oven 60 selects a heating sequence suitable for the food 13 based on the switch input signal and drives and controls the magnetron 4 and the heater 5 following the selected heating sequence. As described in the foregoing, while the conventional microwave oven 60 is capable of sensing the state of the cooked food 13 and weight thereof by using the sensors 8 and 9, it is not capable of distinguish a kind of the food 13. Therefore it is not possible for the oven 60 to automatically select a heating sequence appropriate to the food 13. For cooking the food 13 by the microwave oven 60, therefore, a user should manually operate keys in advance for designating a kind of the food 13. Thoroughly automatic cooking can not be done by the oven 60.
In addition, the thermo fuse used as the abovedescribed safety device takes much time to melt by heat. Thus, when the fuse melts to cut off a power supply path to the above-described heating portion, the temperature in the heating chamber 2 is already increased to a high temperature. As a result, scorched part of the food 13 is so large that it cannot be eaten. In addition, the microwave oven 60 itself is seriously damaged by high temperature. Such makes the user of the oven 60 feel anxious about using the oven and involves maintenance cost for recovering the damage, disadvantage in terms of cost.